This invention relates to flow diverters used in offshore drilling operations and more particularly to movable diverters.
In offshore oilfield drilling operations, a blowout preventer stack 10 is anchored on the ocean floor 12 at a location where the drilling is to occur, as shown in FIG. 1. A floating drilling platform (e.g., a drill ship or semi-submersible platform) 14, which has a rig floor 16, as shown in FIG. 2, from which drilling operations are accomplished, is positioned on the ocean surface 18 above the blowout preventer stack 10. A flow conduit or riser 20, comprising a string of connected joints of pipe, is built between the drilling platform 14 on the surface 18 and the blowout preventer 10 on the ocean floor 12. The riser 20 is built beginning with a single joint of pipe extending through a well center 22, which is an open passage or hole in the rig floor. As each successive joint of pipe is added to the riser 20, the previous joint is passed through the well center 22, extending the riser 20 toward the ocean floor 12. The riser 20 is connected to the blowout preventer stack 10 with a flex joint 24, which allows the riser 20 to change its angular orientation or flex with respect to the blowout preventer stack 10 without causing damage.
Once installation of the riser 20 is completed and drilling operations begin, the riser 20 provides a fluid passageway between the well 26 and the drilling platform 14. For example, the riser 20 may be used to circulate drilling mud between the well 26 and the drilling platform 14. If a gas pocket is encountered during drilling, the gas may enter the well 26 and travel through the riser 20 to the drilling platform 14, where it can be dangerous to people manning the drilling platform 14 and the equipment they use.
To eliminate this danger, a diverter, comprising a diverter housing 28a and a diverter cartridge or insert assembly 28b (shown disassembled in FIG. 2), is connected between the riser 20 and the underside of the rig floor 16. When the diverter insert assembly is installed in the diverter housing, the diverter functions as a multi-position valve which, in one position, allows communication between the riser 20 and the well fluid recovery system on the rig (not shown). In the diverter's other positions, the riser 20 may communicate with one or more exhaust passages 30 (only one is shown) which carry dangerous gas away from the drilling platform 14 and out into the atmosphere where it can disperse harmlessly.
Typically, the diverter is fixed to the underside of the rig floor 16, directly beneath the well center 22. The diverter insert assembly 28b can be removed from the diverter housing 28a, as shown in FIG. 2, and stored outside the rig floor area in the casing rack area 32, but the diverter housing 28a is fixedly attached to the underside of the rig floor 16. Consequently, the riser 20 must slide through the diverter housing 28a, which is only slightly larger in diameter than the riser 20, as the riser 20 is being constructed. The presence of the diverter housing 28a restricts skewing and translation of the riser 20 relative to the rig floor 16 as the riser 20 is being built, which can be a significant problem when seas are rough and the drilling platform 14 is rolling in the seas or where there is a current. When the riser 20 is complete, it is connected to the bottom of the diverter housing via the diverter insert assembly 28b (which includes a flex joint not shown in FIG. 1).